<?php

/**
 * Torrent.
 *
 * PHP version 5.2+ (with cURL extention enabled)
 *
 * 1) Features:
 * - Decode torrent file or data from local file and distant url
 * - Build torrent from source folder/file(s) or distant url
 * - Super easy usage & syntax
 * - Silent Exception error system
 *
 * 2) Usage example
 * <code>
 * require_once 'Torrent.php';
 *
 * // get torrent infos
 * $torrent = new Torrent( './test.torrent' );
 * echo '<br>private: ', $torrent->is_private() ? 'yes' : 'no',
 * '<br>announce: ', $torrent->announce(),
 * '<br>name: ', $torrent->name(),
 * '<br>comment: ', $torrent->comment(),
 * '<br>piece_length: ', $torrent->piece_length(),
 * '<br>size: ', $torrent->size( 2 ),
 * '<br>hash info: ', $torrent->hash_info(),
 * '<br>stats: ';
 * var_dump( $torrent->scrape() );
 * echo '<br>content: ';
 * var_dump( $torrent->content() );
 * echo '<br>source: ',
 * $torrent;
 *
 * // get magnet link
 * $torrent->magnet(); // use $torrent->magnet( false ); to get non html encoded ampersand
 *
 * // create torrent
 * $torrent = new Torrent( array( 'test.mp3', 'test.jpg' ), 'http://torrent.tracker/annonce' );
 * $torrent->save('test.torrent'); // save to disk
 *
 * // modify torrent
 * $torrent->announce('http://alternate-torrent.tracker/annonce'); // add a tracker
 * $torrent->announce(false); // reset announce trackers
 * $torrent->announce(array('http://torrent.tracker/annonce', 'http://alternate-torrent.tracker/annonce')); // set tracker(s), it also works with a 'one tracker' array...
 * $torrent->announce(array(array('http://torrent.tracker/annonce', 'http://alternate-torrent.tracker/annonce'), 'http://another-torrent.tracker/annonce')); // set tiered trackers
 * $torrent->comment('hello world');
 * $torrent->name('test torrent');
 * $torrent->is_private(true);
 * $torrent->httpseeds('http://file-hosting.domain/path/'); // BitTornado implementation
 * $torrent->url_list(array('http://file-hosting.domain/path/','http://another-file-hosting.domain/path/')); //
 * GetRight implementation
 *
 * // print errors
 * if ( $errors = $torrent->errors() )
 * var_dump( $errors );
 *
 * // send to user
 * $torrent->send();
 * </code>
 *
 * @author   Adrien Gibrat <adrien.gibrat@gmail.com>
 * @tester   Jeong, Anton, dokcharlie, official testers ;) Thanks for your precious feedback
 * @copyleft 2010 - Just use it!
 *
 * @license  http://www.gnu.org/licenses/gpl.html GNU General Public License version 3
 *
 * @version  0.0.3
 */
class Torrent
{
  /**
   * @const float Default http timeout
   */
  const timeout = 30;

  /**
   * @var array List of error occurred
   */
  protected static $_errors = [];

  /** Read and decode torrent file/data OR build a torrent from source folder/file(s)
   * Supported signatures:
   * - Torrent(); // get an instance (useful to scrape and check errors)
   * - Torrent( string $torrent ); // analyze a torrent file
   * - Torrent( string $torrent, string $announce );
   * - Torrent( string $torrent, array $meta );
   * - Torrent( string $file_or_folder ); // create a torrent file
   * - Torrent( string $file_or_folder, string $announce_url, [int $piece_length] );
   * - Torrent( string $file_or_folder, array $meta, [int $piece_length] );
   * - Torrent( array $files_list );
   * - Torrent( array $files_list, string $announce_url, [int $piece_length] );
   * - Torrent( array $files_list, array $meta, [int $piece_length] );.
   *
   * @param string|array torrent to read or source folder/file(s) (optional, to get an instance)
   * @param string|array announce url or meta informations (optional)
   * @param int piece length (optional)
   */
  public function __construct($data = null, $meta = [], $piece_length = 256)
  {
    if (is_null($data)) {
      return false;
    }
    if ($piece_length < 32 || $piece_length > 4096) {
      return self::set_error(new Exception('Invalid piece length, must be between 32 and 4096'));
    }
    if (is_string($meta)) {
      $meta = ['announce' => $meta];
    }
    if ($this->build($data, $piece_length * 1024)) {
      $this->touch();
    } else {
      $meta = array_merge($meta, $this->decode($data));
    }
    foreach ($meta as $key => $value) {
      $this->{trim($key)} = $value;
    }
    if (isset($this->info["name.utf-8"])) {
      $this->info["name"] = $this->info["name.utf-8"];
      foreach ($this->info["files"] as $key => &$value) {
        $value["path"] = $value["path.utf-8"];
      }
    }
  }

  /** Convert the current Torrent instance in torrent format
   *
   * @return string encoded torrent data
   */
  public function __toString()
  {
    return $this->encode($this);
  }

  /** Return last error message
   *
   * @return string|bool last error message or false if none
   */
  public function error()
  {
    return empty(self::$_errors) ?
      false :
      self::$_errors[0]->getMessage();
  }

  /** Return Errors
   *
   * @return array|bool error list or false if none
   */
  public function errors()
  {
    return empty(self::$_errors) ?
      false :
      self::$_errors;
  }

  /**** Getters and setters ****/

  /** Getter and setter of torrent announce url / list
   * If the argument is a string, announce url is added to announce list (or set as announce if announce is not set)
   * If the argument is an array/object, set announce url (with first url) and list (if array has more than one url), tiered list supported
   * If the argument is false announce url & list are unset.
   *
   * @param null|false|string|array announce url / list, reset all if false (optional, if omitted it's a getter)
   *
   * @return string|array|null announce url / list or null if not set
   */
  public function announce($announce = null)
  {
    if (is_null($announce)) {
      return !isset($this->{'announce-list'}) ?
        isset($this->announce) ? $this->announce : null :
        $this->{'announce-list'};
    }
    $this->touch();
    if (is_string($announce) && isset($this->announce)) {
      return $this->{'announce-list'} = self::announce_list(isset($this->{'announce-list'}) ? $this->{'announce-list'} : $this->announce, $announce);
    }
    unset($this->{'announce-list'});
    if (is_array($announce) || is_object($announce)) {
      if (($this->announce = self::first_announce($announce)) && count($announce) > 1) {
        return $this->{'announce-list'} = self::announce_list($announce);
      } else {
        return $this->announce;
      }
    }
    if (!isset($this->announce) && $announce) {
      return $this->announce = (string) $announce;
    }
    unset($this->announce);
  }

  /** Getter and setter of torrent creation date
   *
   * @param null|int timestamp (optional, if omitted it's a getter)
   *
   * @return int|null timestamp or null if not set
   */
  public function creation_date($timestamp = null)
  {
    return is_null($timestamp) ?
      isset($this->{'creation date'}) ? $this->{'creation date'} : null :
      $this->touch($this->{'creation date'} = (int) $timestamp);
  }

  /** Getter and setter of torrent comment
   *
   * @param null|string comment (optional, if omitted it's a getter)
   *
   * @return string|null comment or null if not set
   */
  public function comment($comment = null)
  {
    return is_null($comment) ?
      isset($this->comment) ? $this->comment : null :
      $this->touch($this->comment = (string) $comment);
  }

  /** Getter and setter of torrent name
   *
   * @param null|string name (optional, if omitted it's a getter)
   *
   * @return string|null name or null if not set
   */
  public function name($name = null)
  {
    return is_null($name) ?
      isset($this->info['name']) ? $this->info['name'] : null :
      $this->touch($this->info['name'] = (string) $name);
  }

  /** Getter and setter of private flag
   *
   * @param null|bool is private or not (optional, if omitted it's a getter)
   *
   * @return bool private flag
   */
  public function is_private($private = null)
  {
    return is_null($private) ?
      !empty($this->info['private']) :
      $this->touch($this->info['private'] = $private ? 1 : 0);
  }

  /** Getter and setter of torrent source
   *
   * @param null|string source (optional, if omitted it's a getter)
   *
   * @return string|null source or null if not set
   */
  public function source($source = null)
  {
    return is_null($source) ?
      isset($this->info['source']) ? $this->info['source'] : null :
      $this->touch($this->info['source'] = (string) $source);
  }

  /** Getter and setter of webseed(s) url list ( GetRight implementation )
   *
   * @param null|string|array webseed or webseeds mirror list (optional, if omitted it's a getter)
   *
   * @return string|array|null webseed(s) or null if not set
   */
  public function url_list($urls = null)
  {
    return is_null($urls) ?
      isset($this->{'url-list'}) ? $this->{'url-list'} : null :
      $this->touch($this->{'url-list'} = is_string($urls) ? $urls : (array) $urls);
  }

  /** Getter and setter of httpseed(s) url list ( BitTornado implementation )
   *
   * @param null|string|array httpseed or httpseeds mirror list (optional, if omitted it's a getter)
   *
   * @return array|null httpseed(s) or null if not set
   */
  public function httpseeds($urls = null)
  {
    return is_null($urls) ?
      isset($this->httpseeds) ? $this->httpseeds : null :
      $this->touch($this->httpseeds = (array) $urls);
  }

  /**** Analyze BitTorrent ****/

  /** Get piece length
   *
   * @return int piece length or null if not set
   */
  public function piece_length()
  {
    return isset($this->info['piece length']) ?
      $this->info['piece length'] :
      null;
  }

  /** Compute hash info
   *
   * @return string hash info or null if info not set
   */
  public function hash_info()
  {
    return isset($this->info) ?
      sha1(self::encode($this->info)) :
      null;
  }

  public function ed2k()
  {
    $files = [];
    if (isset($this->info['ed2k'])) {
      $file = $this->info;
      // var_dump($file);
      $name = isset($file['name.utf-8']) ? $file['name.utf-8'] : $file['name'];
      $length = $file['length'];
      $hash = isset($file['ed2k']) ? unpack('H*', $file['ed2k'])[1] : '';
      if ('' !== $hash) {
        $files[] = "ed2k://|file|$name|$length|$hash|/";
      }
    }
    if (isset($this->info['files']) && is_array($this->info['files'])) {
      foreach ($this->info['files'] as $file) {
        $name = isset($file['path.utf-8']) ? $file['path.utf-8'][0] : $file['path'][0];
        $length = $file['length'];
        $hash = isset($file['ed2k']) ? unpack('H*', $file['ed2k'])[1] : '';
        if ('' !== $hash) {
          $files[] = "ed2k://|file|$name|$length|$hash|/";
        }
      }
    }

    return $files;
  }

  /** List torrent content
   *
   * @param int|null size precision (optional, if omitted returns sizes in bytes)
   *
   * @return array file(s) and size(s) list, files as keys and sizes as values
   */
  public function content($precision = null)
  {
    $files = [];
    if (isset($this->info['files']) && is_array($this->info['files'])) {
      foreach ($this->info['files'] as $file) {
        $files[self::path($file['path'], $this->info['name'])] = $precision ?
          self::format($file['length'], $precision) :
          $file['length'];
      }
    } elseif (isset($this->info['name'])) {
      $files[$this->info['name']] = $precision ?
        self::format($this->info['length'], $precision) :
        $this->info['length'];
    }

    return $files;
  }

  /** List torrent content pieces and offset(s)
   *
   * @return array file(s) and pieces/offset(s) list, file(s) as keys and pieces/offset(s) as values
   */
  public function offset()
  {
    $files = [];
    $size = 0;
    if (isset($this->info['files']) && is_array($this->info['files'])) {
      foreach ($this->info['files'] as $file) {
        $files[self::path($file['path'], $this->info['name'])] = [
          'startpiece' => floor($size / $this->info['piece length']),
          'offset' => fmod($size, $this->info['piece length']),
          'size' => $size += $file['length'],
          'endpiece' => floor($size / $this->info['piece length']),
        ];
      }
    } elseif (isset($this->info['name'])) {
      $files[$this->info['name']] = [
        'startpiece' => 0,
        'offset' => 0,
        'size' => $this->info['length'],
        'endpiece' => floor($this->info['length'] / $this->info['piece length']),
      ];
    }

    return $files;
  }

  /** Sum torrent content size
   *
   * @param int|null size precision (optional, if omitted returns size in bytes)
   *
   * @return int|string file(s) size
   */
  public function size($precision = null)
  {
    $size = 0;
    if (isset($this->info['files']) && is_array($this->info['files'])) {
      foreach ($this->info['files'] as $file) {
        $size += $file['length'];
      }
    } elseif (isset($this->info['name'])) {
      $size = $this->info['length'];
    }

    return is_null($precision) ?
      $size :
      self::format($size, $precision);
  }

  /** Request torrent statistics from scrape page USING CURL!!
   *
   * @param string|array announce or scrape page url (optional, to request an alternative tracker BUT required for static call)
   * @param string torrent hash info (optional, required ONLY for static call)
   * @param float read timeout in seconds (optional, default to self::timeout 30s)
   *
   * @return array tracker torrent statistics
   */
  /* static */
  public function scrape($announce = null, $hash_info = null, $timeout = self::timeout)
  {
    $packed_hash = urlencode(pack('H*', $hash_info ? $hash_info : $this->hash_info()));
    $handles = $scrape = [];
    if (!function_exists('curl_multi_init')) {
      return self::set_error(new Exception('Install CURL with "curl_multi_init" enabled'));
    }
    $curl = curl_multi_init();
    foreach ((array) ($announce ? $announce : $this->announce()) as $tier) {
      foreach ((array) $tier as $tracker) {
        $tracker = str_ireplace([
          'udp://',
          '/announce',
          ':80/',
        ], [
          'http://',
          '/scrape',
          '/',
        ], $tracker);
        if (isset($handles[$tracker])) {
          continue;
        }
        $handles[$tracker] = curl_init($tracker . '?info_hash=' . $packed_hash);
        curl_setopt($handles[$tracker], CURLOPT_RETURNTRANSFER, true);
        curl_setopt($handles[$tracker], CURLOPT_TIMEOUT, $timeout);
        curl_multi_add_handle($curl, $handles[$tracker]);
      }
    }
    do {
      while (CURLM_CALL_MULTI_PERFORM == ($state = curl_multi_exec($curl, $running)));
      if (CURLM_OK != $state) {
        continue;
      }
      while ($done = curl_multi_info_read($curl)) {
        $info = curl_getinfo($done['handle']);
        $tracker = explode('?', $info['url'], 2);
        $tracker = array_shift($tracker);
        if (empty($info['http_code'])) {
          $scrape[$tracker] = self::set_error(new Exception('Tracker request timeout (' . $timeout . 's)'), true);
          continue;
        } elseif (200 != $info['http_code']) {
          $scrape[$tracker] = self::set_error(new Exception('Tracker request failed (' . $info['http_code'] . ' code)'), true);
          continue;
        }
        $data = curl_multi_getcontent($done['handle']);
        $stats = self::decode_data($data);
        curl_multi_remove_handle($curl, $done['handle']);
        $scrape[$tracker] = empty($stats['files']) ?
          self::set_error(new Exception('Empty scrape data'), true) :
          array_shift($stats['files']) + (empty($stats['flags']) ? [] : $stats['flags']);
      }
    } while ($running);
    curl_multi_close($curl);

    return $scrape;
  }

  /**** Save and Send ****/

  /** Save torrent file to disk
   *
   * @param null|string name of the file (optional)
   *
   * @return bool file has been saved or not
   */
  public function save($filename = null)
  {
    return file_put_contents(is_null($filename) ? $this->info['name'] . '.torrent' : $filename, $this->encode($this));
  }

  /** Send torrent file to client
   *
   * @param null|string name of the file (optional)
   */
  public function send($filename = null)
  {
    $data = $this->encode($this);
    header('Content-type: application/x-bittorrent');
    header('Content-Length: ' . strlen($data));
    header('Content-Disposition: attachment; filename="' . (is_null($filename) ? $this->info['name'] . '.torrent' : $filename) . '"');
    exit($data);
  }

  /** Get magnet link
   *
   * @param bool html encode ampersand, default true (optional)
   *
   * @return string magnet link
   */
  public function magnet($html = true)
  {
    $ampersand = $html ? '&amp;' : '&';

    return sprintf('magnet:?xt=urn:btih:%2$s%1$sdn=%3$s%1$sxl=%4$d%1$str=%5$s', $ampersand, $this->hash_info(), urlencode($this->name()), $this->size(), implode($ampersand . 'tr=', self::untier($this->announce())));
  }

  /**** Encode BitTorrent ****/

  /** Encode torrent data
   *
   * @param mixed data to encode
   *
   * @return string torrent encoded data
   */
  public static function encode($mixed)
  {
    switch (gettype($mixed)) {
      case 'integer':
      case 'double':
        return self::encode_integer($mixed);
      case 'object':
        $mixed = get_object_vars($mixed);
        // no break
      case 'array':
        return self::encode_array($mixed);
      default:
        return self::encode_string((string) $mixed);
    }
  }

  /** Encode torrent string
   *
   * @param string string to encode
   *
   * @return string encoded string
   */
  private static function encode_string($string)
  {
    return strlen($string) . ':' . $string;
  }

  /** Encode torrent integer
   *
   * @param int integer to encode
   *
   * @return string encoded integer
   */
  private static function encode_integer($integer)
  {
    return 'i' . $integer . 'e';
  }

  /** Encode torrent dictionary or list
   *
   * @param array array to encode
   *
   * @return string encoded dictionary or list
   */
  private static function encode_array($array)
  {
    if (self::is_list($array)) {
      $return = 'l';
      foreach ($array as $value) {
        $return .= self::encode($value);
      }
    } else {
      ksort($array, SORT_STRING);
      $return = 'd';
      foreach ($array as $key => $value) {
        $return .= self::encode(strval($key)) . self::encode($value);
      }
    }

    return $return . 'e';
  }

  /**** Decode BitTorrent ****/

  /** Decode torrent data or file
   *
   * @param string data or file path to decode
   *
   * @return array decoded torrent data
   */
  protected static function decode($string)
  {
    $data = is_file($string) || self::url_exists($string) ?
      self::file_get_contents($string) :
      $string;

    return (array) self::decode_data($data);
  }

  /** Decode torrent data
   *
   * @param string data to decode
   *
   * @return array decoded torrent data
   */
  private static function decode_data(&$data)
  {
    switch (self::char($data)) {
      case 'i':
        $data = substr($data, 1);

        return self::decode_integer($data);
      case 'l':
        $data = substr($data, 1);

        return self::decode_list($data);
      case 'd':
        $data = substr($data, 1);

        return self::decode_dictionary($data);
      default:
        return self::decode_string($data);
    }
  }

  /** Decode torrent dictionary
   *
   * @param string data to decode
   *
   * @return array decoded dictionary
   */
  private static function decode_dictionary(&$data)
  {
    $dictionary = [];
    $previous = null;
    while ('e' != ($char = self::char($data))) {
      if (false === $char) {
        return self::set_error(new Exception('Unterminated dictionary'));
      }
      if (!ctype_digit($char)) {
        return self::set_error(new Exception('Invalid dictionary key'));
      }
      $key = self::decode_string($data);
      if (isset($dictionary[$key])) {
        return self::set_error(new Exception('Duplicate dictionary key'));
      }
      if ($key < $previous) {
        self::set_error(new Exception('Missorted dictionary key'));
      }
      $dictionary[$key] = self::decode_data($data);
      $previous = $key;
    }
    $data = substr($data, 1);

    return $dictionary;
  }

  /** Decode torrent list
   *
   * @param string data to decode
   *
   * @return array decoded list
   */
  private static function decode_list(&$data)
  {
    $list = [];
    while ('e' != ($char = self::char($data))) {
      if (false === $char) {
        return self::set_error(new Exception('Unterminated list'));
      }
      $list[] = self::decode_data($data);
    }
    $data = substr($data, 1);

    return $list;
  }

  /** Decode torrent string
   *
   * @param string data to decode
   *
   * @return string decoded string
   */
  private static function decode_string(&$data)
  {
    if ('0' === self::char($data) && ':' != substr($data, 1, 1)) {
      self::set_error(new Exception('Invalid string length, leading zero'));
    }
    if (!$colon = @strpos($data, ':')) {
      return self::set_error(new Exception('Invalid string length, colon not found'));
    }
    $length = intval(substr($data, 0, $colon));
    if ($length + $colon + 1 > strlen($data)) {
      return self::set_error(new Exception('Invalid string, input too short for string length'));
    }
    $string = substr($data, $colon + 1, $length);
    $data = substr($data, $colon + $length + 1);

    return $string;
  }

  /** Decode torrent integer
   *
   * @param string data to decode
   *
   * @return int decoded integer
   */
  private static function decode_integer(&$data)
  {
    $start = 0;
    $end = strpos($data, 'e');
    if (0 === $end) {
      self::set_error(new Exception('Empty integer'));
    }
    if ('-' == self::char($data)) {
      ++$start;
    }
    if ('0' == substr($data, $start, 1) && $end > $start + 1) {
      self::set_error(new Exception('Leading zero in integer'));
    }
    if (!ctype_digit(substr($data, $start, $start ? $end - 1 : $end))) {
      self::set_error(new Exception('Non-digit characters in integer'));
    }
    $integer = substr($data, 0, $end);
    $data = substr($data, $end + 1);

    return 0 + $integer;
  }

  /**** Internal Helpers ****/

  /** Build torrent info
   *
   * @param string|array source folder/file(s) path
   * @param int piece length
   *
   * @return array|bool torrent info or false if data isn't folder/file(s)
   */
  protected function build($data, $piece_length)
  {
    if (is_null($data)) {
      return false;
    } elseif (is_array($data) && self::is_list($data)) {
      return $this->info = $this->files($data, $piece_length);
    } elseif (is_dir($data)) {
      return $this->info = $this->folder($data, $piece_length);
    } elseif ((is_file($data) || self::url_exists($data)) && !self::is_torrent($data)) {
      return $this->info = $this->file($data, $piece_length);
    } else {
      return false;
    }
  }

  /** Set torrent creator and creation date
   *
   * @param any param
   *
   * @return any param
   */
  protected function touch($void = null)
  {
    $this->{'created by'} = 'Torrent RW PHP Class - http://github.com/adriengibrat/torrent-rw';
    $this->{'creation date'} = time();

    return $void;
  }

  /** Add an error to errors stack
   *
   * @param Exception error to add
   * @param bool return error message or not (optional, default to false)
   *
   * @return bool|string return false or error message if requested
   */
  protected static function set_error($exception, $message = false)
  {
    return (array_unshift(self::$_errors, $exception) && $message) ? $exception->getMessage() : false;
  }

  /** Build announce list
   *
   * @param string|array announce url / list
   * @param string|array announce url / list to add (optionnal)
   *
   * @return array announce list (array of arrays)
   */
  protected static function announce_list($announce, $merge = [])
  {
    return array_map(function ($a) {
      return (array) $a;
    }, array_merge((array) $announce, (array) $merge));
  }

  /** Get the first announce url in a list
   *
   * @param array announce list (array of arrays if tiered trackers)
   *
   * @return string first announce url
   */
  protected static function first_announce($announce)
  {
    while (is_array($announce)) {
      $announce = reset($announce);
    }

    return $announce;
  }

  /** Helper to pack data hash
   *
   * @param string data
   *
   * @return string packed data hash
   */
  protected static function pack(&$data)
  {
    return pack('H*', sha1($data)) . ($data = null);
  }

  /** Helper to build file path
   *
   * @param array file path
   * @param string base folder
   *
   * @return string real file path
   */
  protected static function path($path, $folder)
  {
    array_unshift($path, $folder);

    return join(DIRECTORY_SEPARATOR, $path);
  }

  /** Helper to explode file path
   *
   * @param string file path
   *
   * @return array file path
   */
  protected static function path_explode($path)
  {
    return explode(DIRECTORY_SEPARATOR, $path);
  }

  /** Helper to test if an array is a list
   *
   * @param array array to test
   *
   * @return bool is the array a list or not
   */
  protected static function is_list($array)
  {
    foreach (array_keys($array) as $key) {
      if (!is_int($key)) {
        return false;
      }
    }

    return true;
  }

  /** Build pieces depending on piece length from a file handler
   *
   * @param ressource file handle
   * @param int piece length
   * @param bool is last piece
   *
   * @return string pieces
   */
  private function pieces($handle, $piece_length, $last = true)
  {
    static $piece, $length;
    if (empty($length)) {
      $length = $piece_length;
    }
    $pieces = null;
    while (!feof($handle)) {
      if (($length = strlen($piece .= fread($handle, $length))) == $piece_length) {
        $pieces .= self::pack($piece);
      } elseif (($length = $piece_length - $length) < 0) {
        return self::set_error(new Exception('Invalid piece length!'));
      }
    }
    fclose($handle);

    return $pieces . ($last && $piece ? self::pack($piece) : null);
  }

  /** Build torrent info from single file
   *
   * @param string file path
   * @param int piece length
   *
   * @return array torrent info
   */
  private function file($file, $piece_length)
  {
    if (!$handle = self::fopen($file, $size = self::filesize($file))) {
      return self::set_error(new Exception('Failed to open file: "' . $file . '"'));
    }
    if (self::is_url($file)) {
      $this->url_list($file);
    }
    $path = self::path_explode($file);

    return [
      'length' => $size,
      'name' => end($path),
      'piece length' => $piece_length,
      'pieces' => $this->pieces($handle, $piece_length),
    ];
  }

  /** Build torrent info from files
   *
   * @param array file list
   * @param int piece length
   *
   * @return array torrent info
   */
  private function files($files, $piece_length)
  {
    sort($files);
    usort($files, function ($a, $b) {
      return strrpos($a, DIRECTORY_SEPARATOR) - strrpos($b, DIRECTORY_SEPARATOR);
    });
    $first = current($files);
    if (!self::is_url($first)) {
      $files = array_map('realpath', $files);
    } else {
      $this->url_list(dirname($first) . DIRECTORY_SEPARATOR);
    }
    $files_path = array_map('self::path_explode', $files);
    $root = call_user_func_array('array_intersect_assoc', $files_path);
    $pieces = null;
    $info_files = [];
    $count = count($files) - 1;
    foreach ($files as $i => $file) {
      if (!$handle = self::fopen($file, $filesize = self::filesize($file))) {
        self::set_error(new Exception('Failed to open file: "' . $file . '" discarded'));
        continue;
      }
      $pieces .= $this->pieces($handle, $piece_length, $count == $i);
      $info_files[] = [
        'length' => $filesize,
        'path' => array_diff_assoc($files_path[$i], $root),
      ];
    }

    return [
      'files' => $info_files,
      'name' => end($root),
      'piece length' => $piece_length,
      'pieces' => $pieces,
    ];
  }

  /** Build torrent info from folder content
   *
   * @param string folder path
   * @param int piece length
   *
   * @return array torrent info
   */
  private function folder($dir, $piece_length)
  {
    return $this->files(self::scandir($dir), $piece_length);
  }

  /** Helper to return the first char of encoded data
   *
   * @param string encoded data
   *
   * @return string|bool first char of encoded data or false if empty data
   */
  private static function char($data)
  {
    return empty($data) ?
      false :
      substr($data, 0, 1);
  }

  /**** Public Helpers ****/

  /** Helper to format size in bytes to human readable
   *
   * @param int size in bytes
   * @param int precision after coma
   *
   * @return string formated size in appropriate unit
   */
  public static function format($size, $precision = 2)
  {
    $units = [
      'octets',
      'Ko',
      'Mo',
      'Go',
      'To',
    ];
    while (($next = next($units)) && $size > 1024) {
      $size /= 1024;
    }

    return round($size, $precision) . ' ' . ($next ? prev($units) : end($units));
  }

  /** Helper to return filesize (even bigger than 2Gb -linux only- and distant files size)
   *
   * @param string file path
   *
   * @return float|bool filesize or false if error
   */
  public static function filesize($file)
  {
    if (is_file($file)) {
      return (float) sprintf('%u', @filesize($file));
    } elseif ($content_length = preg_grep($pattern = '#^Content-Length:\s+(\d+)$#i', (array) @get_headers($file))) {
      return (int) preg_replace($pattern, '$1', reset($content_length));
    }
  }

  /** Helper to open file to read (even bigger than 2Gb, linux only)
   *
   * @param string file path
   * @param int|float file size (optional)
   *
   * @return resource|bool file handle or false if error
   */
  public static function fopen($file, $size = null)
  {
    if ((is_null($size) ? self::filesize($file) : $size) <= 2 * pow(1024, 3)) {
      return fopen($file, 'r');
    } elseif (PHP_OS != 'Linux') {
      return self::set_error(new Exception('File size is greater than 2GB. This is only supported under Linux'));
    } elseif (!is_readable($file)) {
      return false;
    } else {
      return popen('cat ' . escapeshellarg(realpath($file)), 'r');
    }
  }

  /** Helper to scan directories files and sub directories recursively
   *
   * @param string directory path
   *
   * @return array directory content list
   */
  public static function scandir($dir)
  {
    $paths = [];
    foreach (scandir($dir) as $item) {
      if ('.' != $item && '..' != $item) {
        if (is_dir($path = realpath($dir . DIRECTORY_SEPARATOR . $item))) {
          $paths = array_merge(self::scandir($path), $paths);
        } else {
          $paths[] = $path;
        }
      }
    }

    return $paths;
  }

  /** Helper to check if string is an url (http)
   *
   * @param string url to check
   *
   * @return bool is string an url
   */
  public static function is_url($url)
  {
    return preg_match('#^http(s)?://[a-z0-9-]+(.[a-z0-9-]+)*(:[0-9]+)?(/.*)?$#i', $url);
  }

  /** Helper to check if url exists
   *
   * @param string url to check
   *
   * @return bool does the url exist or not
   */
  public static function url_exists($url)
  {
    return self::is_url($url) ?
      (bool) self::filesize($url) :
      false;
  }

  /** Helper to check if a file is a torrent
   *
   * @param string file location
   * @param float http timeout (optional, default to self::timeout 30s)
   *
   * @return bool is the file a torrent or not
   */
  public static function is_torrent($file, $timeout = self::timeout)
  {
    return ($start = self::file_get_contents($file, $timeout, 0, 11))
      && 'd8:announce' === $start
      || 'd10:created' === $start
      || 'd13:creatio' === $start
      || 'd13:announc' === $start
      || 'd12:_info_l' === $start
      || 'd7:comment' === substr($start, 0, 10) // @see https://github.com/adriengibrat/torrent-rw/issues/32
      || 'd4:info' === substr($start, 0, 7)
      || 'd9:' === substr($start, 0, 3); // @see https://github.com/adriengibrat/torrent-rw/pull/17
  }

  /** Helper to get (distant) file content
   *
   * @param string file location
   * @param float http timeout (optional, default to self::timeout 30s)
   * @param int starting offset (optional, default to null)
   * @param int content length (optional, default to null)
   *
   * @return string|bool file content or false if error
   */
  public static function file_get_contents($file, $timeout = self::timeout, $offset = null, $length = null)
  {
    if (is_file($file) || ini_get('allow_url_fopen')) {
      $context = !is_file($file) && $timeout ?
        stream_context_create(['http' => ['timeout' => $timeout]]) :
        null;

      return !is_null($offset) ? $length ?
        @file_get_contents($file, false, $context, $offset, $length) :
        @file_get_contents($file, false, $context, $offset) :
        @file_get_contents($file, false, $context);
    } elseif (!function_exists('curl_init')) {
      return self::set_error(new Exception('Install CURL or enable "allow_url_fopen"'));
    }
    $handle = curl_init($file);
    if ($timeout) {
      curl_setopt($handle, CURLOPT_TIMEOUT, $timeout);
    }
    if ($offset || $length) {
      curl_setopt($handle, CURLOPT_RANGE, $offset . '-' . ($length ? $offset + $length - 1 : null));
    }
    curl_setopt($handle, CURLOPT_RETURNTRANSFER, 1);
    $content = curl_exec($handle);
    $size = curl_getinfo($handle, CURLINFO_CONTENT_LENGTH_DOWNLOAD);
    curl_close($handle);

    return ($offset && $size == -1) || ($length && $length != $size) ? $length ?
      substr($content, $offset, $length) :
      substr($content, $offset) :
      $content;
  }

  /** Flatten announces list
   *
   * @param array announces list
   *
   * @return array flattened announces list
   */
  public static function untier($announces)
  {
    $list = [];
    foreach ((array) $announces as $tier) {
      is_array($tier) ?
        $list = array_merge($list, self::untier($tier)) :
        array_push($list, $tier);
    }

    return $list;
  }
}
